Everyone knows that a nuclear explosion destroys lots of blocks, right? So I made a nuclear cannon, designed to destroy only in one direction, like so. It might be hard to see, but there is a single opening in the front for the "shot". The "ammo" is one 6-chamber nuclear reactor, fully stocked with quad uranium or mox cells.
I find the cannon can either clear a 3x3 area about 12 deep in front of it, or kill a block 50 blocks away. the tower 51 blocks away was untouched. (the line of reinforced concrete at the bottom / front of the cannon is my ruler)
This would be an AWESOME siege wall breaker, but falls woefully short on range compared to traditional TNT cannons. Now... if someone can time this bad boy to launch TNT, THAT could be pretty neat! (I am not up to the task)